By letting the coronavirus surge through the population with only minimal social distancing measures in place, the U.S. has accidentally become the world's largest experiment in herd immunity.

Why it matters: Letting the virus spread while minimizing human loss is doable, in theory. But it requires very strict protections for vulnerable people, almost none of which the U.S. has established.

The big picture: Cases are skyrocketing, with hospitalizations and deaths following suit in hotspots. Not a single state has ordered another lockdown, even though per capita cases in Florida and Arizona have reached levels similar to New York and New Jersey’s in April.

• Most states never built up the testing, contact tracing and isolation systems it would take to prevent the virus from spreading widely.
• The Trump administration is generally ignoring or downplaying soaring caseloads across the South and West, and is pushing schools to fully reopen in the fall.
• In Florida, where infections, hospitalizations and deaths are surging, Gov. Ron DeSantis "has repeatedly ruled out a sweeping mask mandate or taking the state back into a lockdown to stem the virus, although local governments have acted on their own," per Bloomberg.

Between the lines: Separating older, sicker people from younger, healthier ones while the virus burns through the latter group could be a way to achieve herd immunity — assuming immunity exists — without hundreds of thousands of people dying.

• But the U.S. hasn't adopted such a strategy with any planning or foresight. Although younger people make up a larger portion of coronavirus cases now than they did earlier in the pandemic, vulnerable people still go to work or live with non-vulnerable people.

Yes, but: Some cities and states, particularly in the Northeast, are focused on containing the virus rather than living with it.

Some 250,000 to 370,000 deaths may have been averted between March and May 15 as a result of the statewide stay-at-home orders enacted to mitigate spread of the coronavirus, a study published Thursday in Health Affairs projects.

Why it matters: As you just read, the U.S. has changed strategies since then.

• New modeling suggests the outbreaks could lead to more than 200,000 deaths by the end of year, Axios' Marisa Fernandez writes.

By the numbers: The daily mortality growth rate decreased 6.1% between March 21 and May 15 within the District of Columbia and the 42 states that implemented shelter-in-place orders.

• As many as 750,000 to 840,000 COVID-19 hospitalizations were also avoided during the same time period, based on data collected from 19 states.

Yes, but: The study acknowledges shutdowns are an economic burden that may lead to other causes of death, and are not sustainable over extensive periods.

120 people in Florida died from the novel coronavirus in the prior 24 hours, the state's health department reported on Thursday — the state's highest daily death toll from the coronavirus since the pandemic began.

School districts are taking it upon themselves to help families get connected to the internet as they face down a long future of virtual learning, Axios' Kim Hart reports.

Walgreens lost $1.7 billion in the three-month stretch that ended May 31, as the coronavirus outbreak kept shoppers at home and raised stores' costs.

Starbucks announced Thursday that it will require customers to wear face coverings in all company-owned stores across the U.S. starting July 15.

A coalition of AI groups is forming to produce a comprehensive data source on the coronavirus pandemic for policymakers and health care leaders, Axios' Bryan Walsh reports.

1,018 federal TSA employees have tested positive for the coronavirus, the agency said in data updated on Thursday.

Many politicians and public health officials sounded a similar lockdown refrain in the spring: let's do this right so we only have to do it once, Axios' Dave Lawler writes.

Reality check: While some countries have thus far managed to keep cases under control after opening up, dozens of countries that had initially turned a corner are now seeing a worrying rebound. They have to decide if and how to return to lockdown — and whether their populations will stand for it.

Driving the news: Protesters gathered again last night in Belgrade, Serbia, following two nights of violent clashes. The tumult began after a sudden uptick in cases led President Aleksandar Vučić to announce a new coronavirus curfew.

• Serbia had initially avoided a major outbreak but lifted what had been one of Europe’s strictest lockdowns in early May and began to allow crowds to pack into sporting events and bars. Parliamentary elections also went ahead in June.

Japan has also seen its case count — long strikingly low given its large, dense population — tick upwards in recent weeks.

• Economy Minister Yasutoshi Nishimura denied yesterday that there was any need for a new state of emergency. Reopening plans, including allowing some fans back in stadiums, are moving ahead.

Other countries have been quicker to react to spikes. Melbourne, Australia entered six weeks of lockdown after a record-high 191 infections were recorded in the state of Victoria on Tuesday.

Go deeper.

More young people are being infected with the coronavirus, and even though they're less likely to die from it, experts warn the virus' spread among young adults may further fuel outbreaks across the U.S., Axios' Alison Snyder reports.

Why it matters: Some people in their 20s and 30s face serious health complications from COVID-19, and a surge in cases among young people gives the virus a bigger foothold, increasing the risk of infection for more vulnerable people.

People can transmit the virus without knowing they have it, and younger people, in particular, could be unknowingly spreading the disease.

• A study in Italy, yet to be peer reviewed, found the probability of having symptoms increased with age and that among 20–39-year-olds only about 22% had a fever or respiratory symptoms (compared to about 35% of 60–79-year-olds).

By the numbers: From Arizona to Allegheny County, Pennsylvania, young people increasingly account for COVID-19 cases.

• In Los Angeles County, nearly 50% of cases are now in people under 40 (compared to about 30% in April), per the LA Times.

Where it stands: Young people are still much less likely to be hospitalized or die from the virus than people older than 60.

• Yes, but: They can and do get very sick with the disease — from dangerous blood clots in their lungs to inflammation of the heart, lungs and even brain.
• And the long-term consequences are unknown.

Go deeper.

The spillover of pathogens from animals to humans — driven mainly by human behaviors like urbanization and the demand to eat meat — is increasing and will continue wreaking havoc unless global action is taken, Axios' Eileen Drage O'Reilly reports.

Driving the news: The UN Environment Program issued a report this week outlining steps to prevent spillovers and encouraging governments to adopt a "One Health" approach to humans, animals and the environment.

• Countries need to be all working on the same page and make sure "that the human disease surveillance systems are sophisticated and sensitive enough that they can catch any cases that do spillover to humans," says Julie Fischer, senior technical adviser to the Global Health Security Agenda Consortium.

What can be done: Several scientific experts tell Axios global surveillance is one of the big first steps to prevention.

Background: Zoonotic diseases, or those that originated in animal hosts and transferred to humans, tend to be the ones that lead to pandemics. COVID-19, MERS, Ebola, bird flu and the West Nile virus are just some that have had devastating results.

• The human population has grown from roughly 1.6 billion in 1900 to about 7.8 billion today, stressing the Earth's land and resources.
• Some zoonotic diseases become endemic, regularly killing people.

What to watch: Global scientific collaboration is key — a prong recently weakened by the U.S. announcement that it will leave the WHO.

Go deeper.

Airlines are trying to reassure customers the risk of being infected by the coronavirus on a flight is low because of their improved cleaning efforts and sophisticated cabin ventilation systems, Axios' Joann Muller writes.

Why it matters: The airline industry can't recover until passengers feel it is safe to travel again.

• Health experts largely agree flying is safe, as long as passengers can spread out a bit, writes the Los Angeles Times.

The catch: If you're crammed into a seat next to a sick person — especially if they're not wearing a mask — the risk is higher.

How it works: The air on a plane is exchanged as frequently as 10 to 12 times per hour, writes Harvard public health professor Joseph Allen, author of "Healthy Buildings," in a Washington Post op-ed.

• Air vents above passengers' heads push air downward, not sideways, to vents near the floor, which helps minimize infection from one passenger to another.
• The air is cleaned using sophisticated HEPA filters that capture 99% of germs and viruses, then mixed with fresh air and recirculated every two to three minutes.

What to watch: New technologies being tested will make the ventilation systems even more effective.

Yes, but: Even with proper ventilation, on a crowded plane, it's difficult to avoid your neighbor breathing on you.

• While some airlines are intentionally limiting bookings to allow for social distancing, some low-cost airlines are urging Transportation Department officials not to impose any capacity limits.